Method of producing pure nickel by electrolytic refining



C. CUENOT I March 11, 1969 METHOD OF PRODUCING PURE NICKEL BYELECTROLYTIC REFINING Filed Nov. 27, 1964 Sheet of 2 March 11, 1969 c.CUENOT 3,432,410

METHOD OF PRODUCING PURE NICKEL BY ELECTROLYTIC REFINING Filed Nov. 27,1964 Sheet 2 of 2 United States Patent 3,432,410 METHOD OF PRODUCINGPURE NICKEL BY ELECTROLYTIC REFINING Charles Cuenot, Sainte Suzanne,France, assignor to Le Nickel, Socit Anonyme, Paris, France Filed Nov.27, 1964, Ser. No. 414,091 Claims priority, applicsitiougFrance, Nov.27, 1963,

us. Cl. 204-112 Int. Cl. 'C22d 1/14 16 Claims ABSTRACT OF THE DISCLOSUREThis invention relates in general to the manufacture of high-purity(about 99.95 by weight) nickel from ferronickel and more particularly toa method of producing high-purity nickel cathodes by electrolyticrefining from ferronickel anodes.

It is a primary object of this invention to provide a method ofproducing high-purity electrolytic nickel directly from ferronickelalloys.

Patented Mar. 11, 1969 iron, cobalt, etc., and an anode slime comprisingmainly iron, cobalt, etc.

A chemical treatment of the impure anolyte for removing all the iron,cobalt, etc., thus delivering a purified electrolyte which issubsequently used as a catholyte.

A cathode deposit, the nickel being electrodeposited on metal platessuch as stainless or nickel plates in cathodic compartments from theaforesaid catholyte, the nickelimpoverished catholyte being transferredinto the anodic cells by dilfusion through pervious cloths bounding thecathodic compartment.

If the method is applied by using a high-density current, one fractionof the catholyte must be recirculated with a high output at least equalto 0.66 to 0.8 gallon per hour per amp/hr. and the nickel concentrationin the electrolyte must be relatively high in order to yield asatisfactory homogeneous deposit.

Ferronickel anodes contain mainly nickel and iron. The method isapplicable irrespective of the nickel contents of the anodes; however,for the sake of economy it is desirable to use ferronickel anodes havinga nickel content higher than 80% by weight.

The anode corrosion takes place regularly and uniformly. The weight ofthe noncorroded anode portion may be as low as about '4 to 5% of theinitial weight, without taking into account the anode portion emergingfrom the bath.

By way of example, in the specific case contemplated hereinafter, theanode corrosion for 100 kilograms of ferronickel led to the followingresults concerning the division on the one hand of the elementsdissolved in the anolyte and on the other hand of the elements remainingon the anode in the form of anode wastes, and finally, the elementstransferred to the anode slimes:

AFTER EXHAUSTING 100 KILOGRAMS OF ANODE Anode wastes, elements Anolyte,

Anodes, Anode slimes, elements remaining in the form of elements initialremaining in the anode anode wastes (immersed dissolved composition,slimes portion alone) in the weight anolyte,

kg. Weight kg. Percent Weight kg. Percent weight kg.

88. 80 1. 94 37 4. 20 88. 8 82. 71 1. 20 0. 07 1. 3 O. 06 1. 2 1. 07 0.24 O. 07 1. 3 0. 01 0. 24 0. 16 7. l5 0. 77 14. 8 0. 33 7. l5 6. 05 0.800. 14 2. 64 0. 03 0.80 0. 63 1. 81 2.21 42. 96 0. 07 1. 85

This invention provides a method of forming cathode deposits ofelectrolytic nickel and notably av method of producing electrolyticnickel plates.

The method of this invention is applicable under both low and highcurrent density values; however, a high cathode current density (of theorder of 2,000 to 3,000 amps/sq. ft.) permits of increasing appreciablythe production rate of electrolytic cells and, therefore, of reducingthe corresponding investments.

This invention proposes the use of an aqueous electrolyte affording asatisfactory anode corrosion and a proper cathode deposit.

Other objects and advantageous features of this invention will appearduring the following description of the method constituting the primaryobject thereof.

As a rule, the present invention provides a method of producinghigh-purity electrolytic nickel by electrolytic refining fromferronickel anodes, this method comprising the following steps:

An anodic corrosion of ferronickel anodes in anodic compartmentscontaining a nickel-chloride aqueous electrolyte to form a high-nickelimpure anolyte including The anode slime comprises a light fraction anda heavy fraction. Light slime (about 92% of the slimes) is reddish andhas a high iron content. Heavy slime is black (about 8% of the slimes).By way of example, in a specific case the slimes showed the followingcompositions:

Anode slimes The surface area of the electrodes used in these examples,whether anodes or cathodes, may range from 2 to 13 sq. ft.

The original cathode may be a stainless mother plate the surfaces ofwhich are properly prepared for example by sandblasting so as to beslightly but very regularly rough, the electrodeposition of nickelforming on both faces of this plate a commercial nickel cathode having athickness ranging from A" to A which is separated from the mother plateafter the electrolysis.

The original cathode may also consist of a nickel mother sheet having athickness ranging from about 0.02" to 0.04", obtained byelectrodeposition of nickel on a stainless-steel mother plate andseparation of the thus deposited nickel sheets when their thicknessattains a value of about 0.02" to 0.04"; the internal texture and thesurface of these mother sheets are carefully prepared for example byeffecting the following sequence of operation:

Grinding to remove a surface skin and thus providing a smooth, regularsurface; planishing to obtain a straight, flat sheet, and annealing andstamping to form grooves in the sheet and make it nondeformable; thethus treated sheets are used as mother sheets for producing commercialnickel cathodes of a thickness ranging from about 0.35 to 0.47" andincorporating the mother sheet constituting the intermediate portion ofthe commercial cathode.

This invention is also concerned with commercial nickel cathodesobtained by carrying out the method described hereinabove.

Various types of electrolytic cells may be used for carrying out themethod of this invention.

In the attached drawing, FIGURE 1 is a diagrammatic vertical sectionshowing a specific form of embodiment of an electrolytic cell; FIGURE 2is a similar vertical section but taken at right angles to the former inthe cathode compartment portion of the assembly, and FIGURE 3 is a blockdiagram showing the various steps of an electrolysis carried outaccording to the method of this invention.

The ferronickel anodes are corroded anodically in electrolytic cells 2filled with a nickel-chloride electrolyte to produce a high-nickelimpure anolyte 3.

The impure liquid anolyte produced with a pH approximating 4 containsabout 70 to 85 grams per liter of nickel, 30 to 60 grams per liter ofcalcium, to grams per liter of sodium, about 0.5 to 1 gram per liter ofiron, 0.10 to 0.20 gram per liter of cobalt, 0.010 to 0.020 g am perliter of copper. This concentrated solution is at a temperature of theorder of 45 to 60 (113 F. to 140 F.).

The impure anolyte is treated at 4, outside the electrolytic cell, toremove the greater portion of its iron and cobalt contents, notably inorder to produce a pure catholyte 5 from which electrodeposited nickelcathodes 6 are formed which contain at least 99.85% nickel, less than0.1% cobalt, less than 0.01% iron, less than 0.01% copper. The ironprecipitation takes place under a pH value ranging from 1.8 to 3.5 bychlorine peroxidation in the presence of a precipitation agent whichshould be a basic nickel material such as hydrate or carbonate ofnickel. If hydrate of nickel is used (a product which can be prepared byelectrolysis) an amount of hydrate of nickel which corresponds to thestoichiometric quantity of iron dissolved in the electrolyte should beintroduced. Copper and arsenic are eliminated with iron. Theprecipitation of cobalt takes place under a pH value of 3.5 to 4.5 inthe presence for example of milk of lime and chlorine; calcium andsodium remain in the solution.

The catholyte, that is, the electrolyte of purified aqueous chloride,has a pH value ranging from 4 to 5 set preferably at 4.5, and containsnot more than 0.005 gram/liter of iron, 0.010 gram/liter of cobalt and0.003 gram/liter of copper. The nickel and chlorine radicalconcentrations are practically the same as in the impure anolyte. Thecatholyte is electrolyzed in the cathodic compartment 7 at a temperatureranging from 50 C. to 60 C. (122 F. to 140 F.) by causing electriccurrent to flow therethrough. The current density may be variable;however,

4 very satisfactory results are observed with current density valuesranging from about 1,500 amps/sq. ft. to about 4,500 amps/ sq. ft. Thecatholyte is electrolysed under the above-described conditions betweenthe anode 1 and the cathode 6 and permits of obtaining satisfactorycathodes of electrodeposited nickel. During the electrolysis, apotential ranging from 1.5 to 1.7 volts is maintained between the anodeand cathode.

The use of high-density current, that is, above 1,500 amps/sq. ft. andnotably from 2,000 to 4,500 amps/sq. ft. for electrodepositing nickelimplies the stirring of the catholyte in the cathodic compartment tofacilitate the diffusion through the cathodic film of the nickel ions tobe discharged.

This stirring is obtained by resorting to a forced circulation of thecatholyte along the path 8 in the cathodic compartment 7 by means of acirculation pump (not shown). The recirculated catholyte is perferablyreheated along its path outside the cathodic cell to a temperatureranging from 50 C. to 60 C. (122 F. to 140 F.). The pure catholyte 5from the anolyte purification is fed at 9 to the recirculated catholyte8 and the mixture 12 of the two catholyte streams is reintroduced intothe cathodic compartment 7. To effect a satisfactory nickel depositunder a current density of 3,000 amps/sq. ft., the catholyte circulationoutput should be at least from 0.66 to 0.8 gallon per hr. and peramp/hr. Of course, the catholyte circulation output should be adjustedas a function of the actual density of the current utilized.

Moreover, in order to ensure a proper nickel deposition at currentdensity values higher than 2,000 to 2,500 amps/ sq. ft., suddenvariations in the electrolyte composition should be avoided and minimumcontents of the order of 70 grams/liter of nickel and 40 grams/liter ofcalcium should be adhered to.

In practice, only 10 percent of the nickel contents of the high-nickelpurified catholyte are removed during the electrodeposition of nickel inthe cathodic compartment 7. The nickel-impoverished catholyte will thenflow in the direction of the arrows f through the cathodic cloths 10bounding the anodic compartment 7 in front of the anode 1, towards theanolyte 3 where its nickel and impurity contents increase before flowingout from the cells in the form of impure anolyte 3 which is recirculatedas shown in FIGURE 1.

With a current density of 3,000 amps/ sq. ft. the anodic corrosion andthe cathodic deposit take place with an efiiciency attaining for theanodic current and 95% for the cathodic current.

The following example illustrates a typical and nonlimiting case of anelectrolyte carried out according to the teachings of this invention:

EXAMPLE The electrolysis is carried out in cells 11 (FIGURE 3)comprising sixty-one electrodes, that is, thirty-one anodes 1 and thirtycathodes 6; the rectangular anode dimensions are 30" x 40" with aninitial thickness of 2.16"; the rectangular cathode consists of 32" x42" x 0.2 stainless steel plates. The anodes constitute the raw materialto be treated.

Each cathode 6 is disposed in a cathodic cell 7 consisting of a cathodicbox of polyester reinforced with glass fabric, the two lateral faces ofthis box which register with the anode being hollowed and comprisingcathodic cloths 10 permitting the gravity of a 4.8 cu. in. per houroutput per amp/hr. of catholyte towards the anolyte.

The inner dimensions of the electrolytic cells are 51" x 227" x 55".These cells are lined internally with a corrosion-resistant materialalso adapted to withstand mechanical shocks and heat surges, such aspolyester resin reinforced with glass fabric.

In the diagram of FIGURE 3 only one anode 1 and one cathode 6 is shownin the cell 11 in order to simplify the drawing.

The electrolysis is carried out under a current density of 3,000 amps.per sq. ft., thus giving 450 amperes admitted for each electrode or13,600 amperes per electrolytic cell.

The catholyte 12 is distributed along the cathodes 6 by diffusers in theform of perforated plates 13 (see FIGURE 2) disposed in the cathodicboxes and adapted regularly to sweep the cathodes in the direction ofthe arrows i with an hourly output of 0.66 gallon/hr. per amp/hr. Onefraction of the catholyte (0.0211 gallon/hr. per amp/hr.) is diffusedthrough the cathodic cloths in the direction of the arrows f to theanolyte 3, the remaining catholyte fraction 8 being recirculated to thecathodic boxes 7 after an intermediate reheating in 14 at the rate of0.66 gallon/ hr. per amp/hr. The catholyte is heated at a temperature ofabout 50 C. to 60 C. (122 F. to 140 F.) for example in a steam-heatedgraphite-type heat transfer device. The 50 to 60 C. (122 F. to 140 F.)temperature of the catholyte is one of the factors ensuring a properdeposit of nickel on the cathode.

The anolyte 3 is taken from the electroiytic cells and delivered to thepurifying system at the above-mentioned rate of 4.8 cu. in./hr. peramp/hr.

A cascade set of purifying cells operating continuously permits ofprecipitating iron at 15 (by means of chlorine 16 and hydrate of nickel17) and cobalt at 18 (by means of chlorine 16 and hydrate of lime 19).The reactions, with due regard for the stirrings and recirculations, require a total residence time of about half an hour. By Way ofindication, therefore, given an anolyte output of 15,850 gallons perhour, the reactions take place in six precipitation cells of 158 gallonsuseful capacity each.

The filtration is effected at 20 for example by using filter presseswithout washing the cakes. By way of example, given the above-mentionedoutput and an iron concentration of 1.8 lb. per cu. in. (or 0.5gram/liter) in the anolyte 3 issuing from the electrolytic cells, thefiltration requires three filter presses having a useful surface of 750sq. ft. each, one filter press commencing the filling, the second beingunclogged and the third completing the filling.

The purified anolyte 5 is fed at 9 to the catholyte circuit and theresulting mixture 12 is reintroduced with an hourly output of 0.682gallon per amp/hr. into the cathodic cells 7 from which it flows bygravity from one to the other end of the cathodic boxes. Theabove-mentioned fraction of 4.8 cu. in./hr. per amp/hr. flows throughthe pervious cloths 7 to the anolyte and the remaining fraction 8 of thecatholyte is fed to a circuit from which it is pumped for reheating andeventually recycled.

By way of example, given a catholyte output of 320,000 gallons per hourand an average temperature difference of 5 C. (9 F.), the recirculationcircuit comprises a 3,500 cu. ft. (or 26,400 gallon) storage vat, threepumps having a capacity of 105,000 gaL/hr. each, and a reheatedcatholyte stocking vat having a capacity of 3,500 cu. ft. (or 26,400gallons).

The anode slirnes accumulate in the bottom of cell 11. They are removedperiodically during the idle time period of the cell and collected at21. The anode wastes at the end of the electrolytic process arecollected at 22.

The electrolytic nickel is deposited on 0.2" stainless steel cathodicplates. After height to ten days deposit under a current density of3,000 amps/sq. ft. the cathodic plates coated on each face with a layerof electrolytic nickel having a thickness ranging from A to areextracted from the bath at 23, scoured and washed at 24; the nickelplates are separated from their supporting plates at 25, reannealed inneutral atmosphere to degasify same at 26, and cut to standarddimensions at 27 to yield the final product 28.

Although this invention has been described with reference to favorableand/or optimum conditions, it will be readily understood by anybodyconversant with the art that variations or modifications may becontemplated without departing from the spirit and scope of theinvention. Such variations and modifications are considered as formingan integral part of the invention as set forth in the appended claims.

What I claim is:

1. In a method of producing high-purity nickel by electrolytic refiningwhich comprises the steps of corroding ferronickel anodes in an aqueousnickel-chloride electrolyte contained in the anodic compartment of adivided electrolytic cell for producing a high-nickel impure anolytecontaining impurities, and applying a chemical treatment to said impureanolyte outside said electrolytic cell with a view to form a purifiedelectrolyte fed as a catholyte into the cathodic compartment of saidelectrolytic cell, said cathodic compartment comprising walls ofpervious cloths, electrodepositing the nickel from said catholyte on thecathode, and causing said nickel-impoverished catholyte to pass intosaid anodic compartment by diffusion through said pervious cloths, theimprovements consisting in that said ferronickel anodes have a nickelcontent greater than by weight, that said nickel-chloride anolytecontains per liter about 70 to grams of nickel ions, about 30 to 60grams of calcium ions and about 15 to 20 grams of sodium ions, theanions of said anolyte consisting essentially of chloride ions, thatsaid anolyte has a pH value of about 4 and a temperature ranging from 45to 60 C. (113 F. to F.), and that said catholyte has the same nickel,calcium, sodium and chloride ion contents as said anolyte, a pH valueranging from 4 to 5 and a temperature ranging from 50 C. to 60 C. (122F. to 140 F.).

2. An improved method as set forth in claim 1, wherein said electrolyticcell comprises a plurality of anodes and a plurality of cathodesdisposed in as many cathodic compartments.

3. An improved method as set forth in claim 1, wherein the chemicaltreatment of said impure anolyte comprises the steps of precipitatingthe iron, copper and arsenic at a pH value hanging from 1.8 to 3.5 bychlorine peroxidation in the presence of a basic nickel compound,precipitating the cobalt at a pH value ranging from 3.5 to 4.5 by usingchlorine and milk of lime, and separating the precipitates byfiltnation, the filtrate being used as a catholyte and having a pH valueranging from 4 to 5 and a nickel content of about 70 to 85 grams perliter.

4. A method as set forth in claim 1, wherein the original cathodeconsists of a stainless steel mother plate, the electrodeposition ofnickel forming on each face of said mother plate a commercial nickelcathode having a thickness of M1" to 7 which is separated from themother plate upon completion of the electrolysis.

5. A method as set forth in claim 1, wherein said original cathode is anickel mother sheet having a thickness of about 0.02 to 0.04", obtainedby electrodepositing nickel on a stainless steel mother plate andseparating the deposited nickel sheets when their thickness attains from0.02" to 0.04", said sheets being used as mother sheets for producingcommercial nickel cathodes of a thickness of about 0.35" to 0.47"incorporating the mother sheet constituting the intermediate portion ofsaid commercial cathode.

6. A method as set forth in claim 1, wherein the surface area of theanode and cathode electrodes used ranges from 2. 15 to 13 sq. ft.

7. In a method of producing high-purity nickel by electrolytic refiningwhich comprises the steps of corroding ferronickel anodes in an aqueousnickel-chloride electrolyte contained in the anodic compartment of :adivided electrolytic cell for producing a high-nickel impure anolytecontaining impurities, and applying a chemical treatment to said impureanolyte outside said electrolytic cell with a view to form a purifiedelectrolyte fed as a catholyte into the cathodic compartment of saidelectrolytic cell, said cathodic compartment comprising walls ofpervious cloths, electrodepositing the nickel from said catholyte on thecathode, and causing said nickel-impoverished catholyte to pass intosaid anodic compartment by diffusion through said pervious cloths, theimprovements consisting in that said ferronickel anodes have a nickelcontent greater than 80% by weight, that said nickel-chloride anolytecontains per liter about 70 to 85 grams of nickel ions, about 30 to 60grams of calcium ions and about to grams of sodium ions, the anions ofsaid anolyte consisting essentially of chloride ions, that said anolytehas a pH value of about 4 and a temperature ranging from 45 to 60 C.(113 F. to 140 F.), and that said catholyte has the same nickel,calcium, sodium and chloride ion contents as said anolyte, a pH valueranging from 4 to 5 and a temperature ranging from 50 C. to 60 C. (122F. to 140 F.), that said catholyte is recycled in said cathodiccompartment whereby it will sweep the cathode faces, is reheated duringits recycling to a temperature ranging from 50 to 60 (122 to 140 F.) andelectrolyzed in said cathodic compartment with a current density rangingfrom about 1,500 to about 4,500 amps/ sq. ft.

8. An improved method as set forth in claim 7, wherein said currentdensity is of 3,000 amps/sq. ft. and the catholyte circulation output isat least 0.66 to 0.8 gallon/ hr. per amp/ hr.

9. An improved method as set forth in claim 8, wherein said electrolyticcell comprises a plurality of anodes and a plurality of cathodesdisposed in as many cathodic compartments.

10. An improved method as set forth in claim 8, wherein said chemicaltreatment of the impure anolyte comprises the steps of precipitating theiron, copper and arsenic at a pH value of 1.8 to 3.5 by chlorineperoxidation in the presence of a nickel basic compound, precipitatingthe cobalt at a pH value of 3.5 to 4.5 by using chlorine and milk oflime, and separating the precipitates by filtration, the filtrate beingused as a catholyte having a pH value ranging from 4 to 5 and a nickelcontent of about 70 to 85 grams per liter.

11. An improved method as set forth in claim 7, wherein saidelectrolytic cell comprises a plurality of anodes and a plurality ofcathodes disposed in as many cathodic compartments.

12. An improved method as set forth in claim 7, wherein the chemicaltreatment of said impure anolyte comprises the steps of precipitatingthe iron, copper and arsenic at a pH value of 1.8 to 3.5 by chlorineperoxidation in the presence of a basic nickel compound, precipitatingthe cobalt at a pH value of 3.5 to 4.5 by using chlorine and milk oflime, and separating the precipitates by filtration, the filtrate beingused as a catholyte having a pH value ranging from 4 to 5 and a nickelcontent of about to grams per liter.

13. A method as set forth in claim 7, wherein the original cathodeconsists of a stainless steel mother plate, the electrodeposition ofnickel forming on each face of said mother plate a commercial nickelcathode having a thickness of A to which is separated from the motherplate upon completion of the electrolysis.

14.. A method as set forth in claim 7, wherein said original cathode isa nickel mother sheet having a thickness of about 0.02 to 0.04, obtainedby electrodepositing nickel on a stainless steel mother plate andseparating the deposited nickel on a stainless steel mother plate andseparating the deposited nickel sheets when their thickness attains from0.02" to 0.04", said sheets being used as mother sheets for producingcommercial nickel cathodes of a thickness of about 0.35" to 0.47"incorporating the mother sheet constituting the intermediate portion ofsaid commercial cathode.

15. A method as set forth in claim 7, wherein the surface area of theanode and cathode electrodes used ranges from 2.15 to 13 sq. ft.

16. An aqueous catholyte for producing high-purity electrolytic nickel,containing about 70 to 85 grams of nickel ions, about 30 to 60 grams ofcalcium ions and about 15 to 20 grams of sodium ions per liter, theanions of said catholyte consisting essentially of chloride ions, saidcatholyte having a pH value ranging from 4 to 5.

References Cited UNITED STATES PATENTS 1,251,511 1/1918 Guess 2041l21,887,037 11/1932 Peek et a1 204-112 2,066,347 1/ 1937 Gronningsaeter204-112 2,394,874 2/1946 Renzoni 204-113 2,478,189 8/ 1949Gronningsaeter 204--112 2,597,296 5/1952 Cook et al 204--l12 2,839,4616/ 1958 Renzoni et a1. 2041 13 3,114,687 12/1963 Brandt 204-49 XR ROBERTK. MIHALEK, Primary Examiner.

G. KAPLAN, Assistant Examiner.

US. Cl. X.R. 204-113

